US11160566B2 - Surgical rotational cutting tool and method - Google Patents

Abstract

A surgical rotational cutting tool, a surgical kit and a method of preparing a femur to receive a stem of a femoral prosthetic. The tool includes a longitudinal axis and a shaft extending along the longitudinal axis, which has a proximal end and a distal end. The tool also includes a head located at the distal end of the shaft. The head includes a pointed distal tip, a bone contacting outer surface having a portion which curves inwards toward the longitudinal axis as it approaches the tip, and a plurality of flutes. The edges of distal parts of neighboring pairs of the flutes meet to define a plurality of cutting edges which extend proximally from the pointed distal tip. A proximal part of each flute extends proximally across the curved portion.

Description

CROSS REFERENCE TO RELATED PCT APPLICATION

This application is a National Stage 35 U.S.C. 371 of International Patent Application PCT/EP2018/051682 filed Jan. 24, 2018, which claims priority to United Kingdom Application No. GB1702404.3, filed Feb. 14, 2017.

FIELD OF THE INVENTION

This invention relates to a surgical rotational cutting tool. The invention also relates to a surgical kit comprising at least one surgical rotational cutting tool. This invention further relates to a method of preparing a femur to receive a stem of a femoral prosthetic.

BACKGROUND OF THE INVENTION

Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant. As part of the hip replacement procedure, the femoral head is replaced with a femoral prosthetic that includes a stem, which is inserted into the medullary canal at a proximal end of the femur. The femoral prosthetic also includes a bearing surface, which is received within the acetabulum of the patient. The procedure may in some cases also involve inserting an acetabular cup into the acetabulum of the patient, for receiving the bearing surface of the femoral prosthetic.

To prepare the femur to receive the femoral prosthetic, a cut is made at the proximal end of the femur, to remove the femoral neck and head. Thereafter tools such as drills and reamers are used to first gain access to the medullary canal and then to remove bone from the surface of the canal so as to shape it to receive the stem of the femoral prosthetic.

More particularly, a surgical rotational cutting tool having a sharp tip may first be used to drill into the proximal cut surface of the femur to gain access to the canal. Thereafter, a tool such as an elongate reamer, which typically includes cutting edges located along its side surfaces, may then be used to remove bone from the sidewalls of the medullary canal until it is appropriately shaped to receive the stem. This step may include removing bone from the sides of the entrance to the medullary canal, to widen it. This step may also include removing a part of the greater trochanter that may remain at the proximal end of the femur following the cutting away of the femoral neck and head.

DE 19850980 A1 describes a reamer that has two straight, double-edged, longitudinally adjacent bits with longitudinal axis sloping towards each other. A number of blades run parallel with the longitudinal axes. The peripheral surface between the two blades is concave. The blades extend of the entire proximal part and over the adjacent part of the distal part.

US 2006/127847 A1 describes a rotating instrument made of a ceramic material and comprising a shaft and a working member which is secured to the shaft or can detachably be secured thereto, wherein at least part of the working member is made from a ceramic material.

US 2011/319895 A1 describes an awl that provides for creating an accurate hole in a bone, such as for implantation of a suture anchor. The awl comprises an elongated shaft having a distal tip which terminates in a sharp point adapted to penetrate bone. At least one cutting flute is provided on the shaft and has a longitudinally extending cutting edge formed on the shaft proximal to and adjacent to the sharp point whereby to allow removal of bone via the cutting flute upon rotation of the shaft about a central longitudinal axis thereof inside of the bone.

US 2016/106441 A1 describes a bone access instrument comprising a shaft having a first shaft portion and a second shaft portion. The first shaft portion has a first diameter, a proximal end, a tapered distal end including at least three straight cutting edges being equally spaced circumferentially about the tapered distal end, and at least three flutes extending from the tapered distal end toward the proximal end in a parallel relationship to one another. The second shaft portion has a second diameter and a tapered distal end. The second diameter is less than the first diameter, and the second shaft portion extends axially from the distal end of the first shaft portion.

US 2015/025559 A1 describes a surgical bur that includes a body and a drill point. The body includes flutes and lands. Each of the flutes includes a cutting edge, a rake face, and a clearance surface. Each of the lands is convex-shaped and disposed between a pair of the flutes. The drill point includes axial relief surfaces. Each of the axial relief surfaces has a planar area, is distinct from the lands and borders (i) a distal portion of one of the cutting edges, (ii) one of the lands, and (iii) one of the clearance surfaces.

US 2008/132929 A1 describes a surgical bur including a shaft with a bur head. A number of flutes are formed on the bur head. Each flute has a cutting edge. The flutes are formed so that some of the flutes having cutting edges emerge from the bur head at locations relatively close to the distal end tip of the head. Still other flutes are formed so as to have cutting edges that start, extend proximally rearward, from locations that are, spaced proximal from the distal end tip.

WO 2007/010389 A1 describes a surgical bur including a shaft with a bur head. A number of flutes are foil led on the bur head. Each flute has a cutting edge. The flutes are formed so to have cutting edges extend variable lengths along the outer surface of the bur head.

WO 2014/143597 A1 describes a retro guidewire reamer includes a cutting member, and a mechanism for moving the cutting member from a closed position to a deployed position in a single manual motion. Once a desired size of a bone tunnel is established, a surgeon uses the reamer to create a primary bone tunnel over a guidewire from the outside in. The surgeon retracts the guidewire, and activates the mechanism to deploy the cutting member within the bone joint to conform to the size of a tendon graft. The surgeon uses the deployed cutting member to create a counter bore through the bone in a retrograde manner. Once the counter bore is drilled, the surgeon activates the mechanism to close the cutting member, allowing the reamer to be withdrawn through the primary tunnel. The retro guidewire reamer can be used to provide more accurate bone tunnel placement during ligament reconstruction surgery

WO 2004/014241 A1 describes a drill bit comprising: a shaft which has a pyramidal shaped end defining a drill tip with a plurality of edges defining the pyramidal shape; and one or more recesses for directing away debris produced whilst drilling, the or each recess having a first portion extending along the shaft and a second portion which extends along the drill tip, wherein the second portion of the or each recess extends along an edge of the drill tip.

SUMMARY OF THE INVENTION

Aspects of the invention are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims.

According to an aspect of the invention, there is provided a surgical rotational cutting tool comprising:

a longitudinal axis;

a shaft extending along the longitudinal axis and having a proximal end and a distal end; and

a head located at the distal end of the shaft, the head comprising:

• • a pointed distal tip;
  • a bone contacting outer surface having a curved portion which curves inwards toward the longitudinal axis as it approaches the tip; and
  • a plurality of flutes positioned circumferentially around the head, wherein each flute includes a proximal part and a distal part, wherein each distal part extends proximally from the pointed distal tip, wherein the edges of the distal parts of neighbouring pairs of said circumferentially positioned flutes meet to define a plurality of cutting edges which extend proximally from the pointed distal tip, and wherein the proximal part of each flute extends proximally across the curved portion of the bone contacting outer surface.

The pointed distal tip and cutting edges, which extend proximally therefrom, can be used to cut or drill directly into bone. The inwardly curving bone contacting outer surface, across which the proximal part of each flute extends can act to inhibit the lateral removal of bone by the head when the tool is moved laterally within the bone. This can allow a surgeon to use the tool more safely and precisely, particularly in situations where he or she wants to avoid any lateral drilling/cutting of the bone by the head of the tool when it is inside the bone. In particular, because the proximal parts of each flute extend proximally across the curved portion of the bone contacting outer surface, the edges of these parts of the flutes may be relatively shallow, particularly compared to the sharper cutting edges formed by the edges of distal parts of the flutes, whereby they would are unable to cut laterally into a surface of the bone. Also, the curve of the bone contacting outer surface presents a rounded surface at the sides of the head, which may inhibit the lateral removal of bone by the head even when the lateral movement within the bone involves rotation of the head within a plane containing the longitudinal axis of the tool.

In some examples, a plurality of further cutting edges may be located on the shaft intermediate the head and the proximal end of the shaft. These further cutting edges may be used to make lateral cuts into the bone at a position located proximally with respect to the head. These cuts can be made by moving the tool laterally within the bone, so as to urge the further cutting edges laterally against the surface of the bone. Because the head, as discussed above, has features which prevent lateral drilling/cutting by the head when it is inside the bone, the lateral removal of bone by the further cutting edges located on the shaft can be performed in a controlled manner. In particular, the surgeon need not worry about the lateral movements of the tool for urging the further cutting edges against the bone causing any unwanted removal of bone by the head. Moreover, it is envisaged that the surgeon may use the head as a non-cutting pivot point to leverage the plurality of further cutting edges located on the shaft against the surface of the bone.

Thus, embodiments of this invention can allow the functions of a pointed tip for initially cutting or drilling into a bone, and a lateral reamer, to be combined in a single surgical rotational cutting tool. This can save manufacturing costs in the production surgical instruments for performing a surgical procedure, and can reduce the weight and size of a surgical kit incorporating the tool.

One example of the use of a tool according to an embodiment of this invention may be during a hip replacement procedure, for preparing a femur to receive a stem of a femoral prosthetic. In particular, the pointed distal tip and cutting edges, which extend proximally from the tip, can be used to cut or drill into the proximal cut surface of a femur to gain access to the medullary canal. Thereafter, with the head of the tool located inside the medullary canal, the further cutting edges noted above may be used to remove bone from the sidewalls of the medullary canal until it is appropriately shaped to receive broaches and then the stem. This may include removing bone from the sides of the entrance to the medullary canal, to widen it, and/or removing a part of the greater trochanter that may remain at the proximal end of the femur following the cutting away of the femoral neck and head.

In some embodiments, the angle(s) at which the edges of the distal parts of said neighbouring pairs of flutes meet to define the plurality of cutting edges are more acute than the angle(s) at the edges formed between the proximal part of each flute and the bone contacting outer surface. As noted above, the relative shallowness of the edges formed between the proximal part of each flute and the bone contacting outer surface can prevent them from cutting laterally into a surface of the bone.

The cutting edges extending proximally from the pointed distal tip may be concave. Each flute may have a concave surface. The concave surface may be a concave cylindrical surface. This can conveniently allow the head of the tool to be formed using a cylindrical milling cutter or ball nose cutter, for forming the flutes and the pointed distal tip. Other cross sectional shapes for the flutes (e.g. V-shaped, or square-shaped) are envisaged. Where the cross sectional shape of the flutes is e.g. V-shaped, or square-shaped, an end mill cutter may be used to form them instead. An axis (e.g. a cylindrical axis) of the concave (e.g. cylindrical) surface of each flute may be oriented at an angle in therange 20°≤θ≤80° with respect to the longitudinal axis. This may be implemented by appropriate orientation of a cylindrical milling cutter or appropriate movement of a ball nose cutter during manufacture. The path of each flute as it extends proximally from the distal tip may be substantially straight, although it is also envisaged that the path may be curved. It is also envisaged that each flute may be tilted or angled in one direction to create edges with different angles at either side of the groove formed by each flute. This may allow the cutting edges of each flute to have a preferential rotation cutting direction compared to the opposite rotational direction. Moreover, the groove shape or tilt may change across the surface of the head, to further vary the edge angle.

The proximal parts of respective neighbouring pairs of flutes may be separated from each other by a respective part of the curved portion of the bone contacting outer surface. Each respective part of the curved portion of the bone contacting outer surface may be substantially V-shaped. The apex of each substantially V-shaped part may meet a proximal end of the cutting edge that is defined by the respective neighbouring pair of flutes. Because the apex of the V-shaped part is located on the portion of the bone contacting outer surface that curves inwards toward the longitudinal axis as it approaches the tip, the point formed by the apex of the substantially V-shaped part and the proximal end of the cutting edge that is defined by the respective neighbouring pair of flutes is less sharp than it would otherwise be. This can prevent the apex from cutting laterally into a bone in contact with the bone contacting outer surface.

The bone contacting outer surface may have a proximal portion that curves inwards toward the longitudinal axis with increasing distance from the pointed distal tip, to form a neck of the tool. The proximal part of each flute may extend proximally across the proximal portion of the bone contacting outer surface. This arrangement can allow the flutes to dispense bone that has been cut away by the cutting edges of the head to be dispensed proximally, to the rear of the head.

At least part of the bone contacting outer surface may be substantially spherical. It is envisaged that this may be the optimal shape for inhibiting the lateral removal of bone by the head even when lateral movement of the tool within the bone involves rotation of the head within a plane containing the longitudinal axis of the tool, as discussed above.

The flutes are equally circumferentially spaced around the head. The tool may have exactly four flutes.

The surgical rotation cutting tool may be implemented as, or in, a number of different kinds of surgical instrument. By way of example only, it is envisaged that the surgical rotation cutting tool may be a surgical drill bit, a rotary initiator device (also known as a canal initiator tip), or a straight reamer.

According to another aspect of the invention, there is provided a surgical kit comprising a plurality of surgical rotational cutting tools of the kind set out above. At least one of the surgical rotational cutting tools may be of a different size to at least one other of the surgical rotational cutting tools. The kit may, for instance be for a hip replacement procedure.

According to a further aspect of the invention, there is provided a method of preparing a femur to receive a stem of a femoral prosthetic, the method comprising:

cutting away the head and neck of the femur; and

using a surgical rotational cutting tool of the kind set out above to cut into a proximal cut surface of the femur to gain access to the medullary canal.

As noted above, the tool may include a plurality of further cutting edges located on the shaft and proximally with respect to the head. In such examples, the method may also include positioning the tool so that the head is located inside the medullary canal while the further cutting edges are located at the entrance to the medullary canal. The method may further include moving the tool laterally to use the plurality of further cutting edges to remove bone to widen the entrance to the medullary canal.

The method may also include moving the tool laterally to use the plurality of further cutting edges to remove at least part of the greater trochanter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which:

FIGS. 1 and 2 show two views of a surgical rotational cutting tool according to an embodiment of this invention;

FIG. 3 shows a detailed view of the head of the tool ofFIGS. 1 and 2;

FIG. 4 illustrates a stage in the manufacturing of the surgical rotational cutting tool ofFIGS. 1 to 3, prior to the formation of the flutes of the tool;

FIG. 5A to 5D show a number of cross sections of the surgical rotational cutting tool ofFIGS. 1 to 3, each cross section taken in a plane perpendicular to the longitudinal axis of the tool;

FIG. 6 illustrates the use of a surgical rotational cutting tool of the kind described inFIGS. 1 to 4 in accordance with an embodiment of this invention;

FIGS. 7 and 8 show two views of a surgical rotational cutting tool according to another embodiment of this invention;

FIG. 9 shows a detailed view of the head of the surgical rotational cutting tool ofFIGS. 7 and 8;

FIG. 10 illustrates a stage in the manufacturing of the surgical rotational cutting tool ofFIGS. 7 to 9, prior to the formation of the flutes of the tool; and

FIGS. 11A to 11D show a number of cross sections of the surgical rotational cutting tool ofFIGS. 7 to 9, each cross section taken in a plane perpendicular to the longitudinal axis of the tool.

DETAILED DESCRIPTION

Embodiments of the present invention are described in the following with reference to the accompanying drawings.

Embodiments of this invention can provide a surgical rotation cutting tool, a surgical kit including one or more such tools, and to a method for using such a tool in the preparation of a femur to receive a stem of a femoral prosthetic. The examples shown in the figures relate particularly to a surgical rotation cutting tool that comprises a surgical drill bit. However, it is envisaged that a surgical rotation cutting tool having features of the kind described herein may be implemented as, or in, a number of different kinds of surgical instrument. For instance, it is envisaged that a surgical rotation cutting tool may be implemented as a rotary initiator device (also known as a canal initiator tip), or a straight reamer.

FIG. 1 shows a side view of asurgical drill bit10 for a bone drill according to an embodiment of this invention. An isometric view of thedrill bit10 is shown inFIG. 2.

Thedrill bit10 has a longitudinal axis, which is indicated inFIGS. 1 and 2 by the dotted line labelled5. Thedrill bit10 also has ashaft4. Theshaft4 may be elongate. Theshaft4 extends along thelongitudinal axis5. The shaft has aproximal end2. The proximal end may be attachable to a bone drill. Theproximal end2 may form a shank, as shown inFIGS. 1 and 2. To attach thedrill bit10 to the bone drill, the shank may be received in a chuck of the bone drill. Thedrill bit10 also includes a distal end. As shown in the Figures, thedrill bit10 has ahead6, which is located at the distal end of theshaft4. Thehead6 may be used to drill into the surface of a bone, typically by pressing thehead6 against the bone, in a direction along thelongitudinal axis5.

FIG. 3 shows a detailed view of thehead6 of thedrill bit10.

Thehead6 has a pointeddistal tip8. The pointeddistal tip8 is typically the first part of thedrill bit10 encounter the surface of a bone as thedrill bit10 drills into it. The pointeddistal tip8 may typically be sharp, so as to aid the entrance of thehead6 into the bone.

Thehead6 also includes a plurality offlutes12. In the present example, thehead6 includes fourflutes12A,12B,12C,12D, although it is envisaged that a greater number or fewer number offlutes12 may be provided. Eachflute12A,12B,12C,12D is positioned circumferentially around thehead6. For instance, theflutes12A,12B,12C,12D may be evenly spaced around the circumference of thehead6.

Eachflute12A,12B,12C,12D includes adistal part17 and aproximal part19. As can be seen best inFIG. 3, eachdistal part17 of eachflute12A,12B,12C,12D extends proximally from the pointeddistal tip8. As is also shown inFIG. 3, the edges of thedistal parts17 of neighbouring pairs of theflutes12A,12B,12C,12D meet to define a plurality of cutting edges30. The cutting edges30 each extend proximally from the pointeddistal tip8. For instance, in the present example, the edges of a first pair offlutes12A,12B meet to form afirst cutting edge30, the edges of a second pair offlutes12B,12C meet to form asecond cutting edge30, the edges of a third pair offlutes12C,12D meet to form athird cutting edge30, and the edges of a fourth pair offlutes12D,12A meet to form afourth cutting edge30.

In the present example, the surface of eachflute12A,12B,12C,12D has the shape of a partial cylinder (this is discussed in more detail below in relation toFIG. 4). The cylindrical shape of the surfaces of theflutes12A,12B,12C,12D gives rise to cutting edges which are concave, as is visible inFIG. 3. This curvature of the cutting edges30 lead to a slightly sharper tip, owing the reduction in the angle of thecutting edge30 relative to thelongitudinal axis5 at positions closer to the pointeddistal tip8.

In use, the cutting edges30 rotate about thelongitudinal axis5, cutting into the bone as they do so. Theflutes12A,12B,12C,12D generally act to dispense bone that has been cut away by the cutting edges30 to the rear of thehead6, providing space for further bone to be removed.

Thehead6 also includes a bone contactingouter surface20. The bone contactingouter surface20 has acurved portion21, which curves inwards toward thelongitudinal axis5 as it approaches the pointeddistal tip8. The curvature of thecurved portion21 of the bone contactingouter surface20, as viewed in a plane containing thelongitudinal axis5 may be substantially circular. Theproximal part19 of eachflute12A,12B,12C,12D extends proximally across thiscurved portion21 of the bone contactingouter surface20, as can be seen inFIG. 3. Theedges32 between theproximal parts19 of eachflute12A,12B,12C,12D may be curved (e.g. substantially elliptical).

The inwardly curvingportion21 of the bone contactingouter surface20, across which theproximal part19 of eachflute12A,12B,12C,12D extends can act to inhibit the lateral removal of bone by thehead6 when thedrill bit10 is moved laterally within the bone. This can allow a surgeon to use thedrill bit10 more safely and precisely, particularly in situations where he or she wants to avoid any lateral drilling/cutting of the bone by thehead6.

In particular, because theproximal parts19 of eachflute12A,12B,12C,12D extend proximally across thecurved portion21 of the bone contactingouter surface20, theedges32 of theseparts19 of theflutes12A,12B,12C,12D may be relatively shallow, particularly compared to the cutting edges30. Theedges32 may therefore be unable to cut laterally into a surface of the bone as the drill bit rotates around thelongitudinal axis5. Also, the curve of the bone contactingouter surface20 may present a rounded surface at the sides of thehead6, which may inhibit the lateral removal of bone by thehead6 even when the drill bit is rotated within a plane containing thelongitudinal axis5, as with be discussed below in relation toFIG. 6.

As can be seen inFIG. 3, in the present example, theproximal parts19 of respective neighbouringpairs12A,12B;12B,12C;12C,12D;12D,12A offlutes12 are separated from each other by arespective part34 of thecurved portion21 of the bone contactingouter surface20. Eachrespective part34 of thecurved portion21 of the bone contactingouter surface20 may be substantially V-shaped. The apex36 of each substantially V-shapedpart34 may meet a proximal end of thecutting edge30 that is defined by the edges of thedistal parts17 of the respectiveneighbouring pair12A,12B;12B,12C;12C,12D;12D,12A offlutes12. Note that because thecurved portion21 of the bone contactingouter surface20 curves inwards toward thelongitudinal axis5 as it approaches the pointeddistal tip8, the apex36 is made less prominent at the lateral sides of thehead6 that it would otherwise be. This can significantly reduce the tendency of thehead6 to cut laterally into the bone as the drill bit is moved laterally, e.g. rotated within a plane containing thelongitudinal axis5.

In the present example, the bone contactingouter surface20 also includes a proximal portion that curves inwards toward thelongitudinal axis5 with increasing distance from the pointeddistal tip8, thereby to form aneck18 of thesurgical drill bit10. Theneck18 is located proximal thehead6. In such examples, theshaft4 of thesurgical drill bit10 may be narrower than thehead6. This has the potential benefit of providing a space to the rear of thehead6 to receive bone material that is dispensed there by the flutes. In this respect, note that it is envisaged that theproximal part19 of eachflute12A,12B,12C,12D may extend proximally across the proximal portion of the bone contactingouter surface20 as can be seen inFIG. 3. It is also envisaged that the relativelynarrow shaft4 may comprise a flexible portion, allowing thedrill bit10 to travel around one or more bends inside the bone.

FIG. 4 illustrates a stage in the manufacturing of the surgical drill bit ofFIGS. 1 to 3, prior to the formation of theflutes12A,12B,12C,12D. It is envisaged that the same or a similar approach may be used for manufacturing other surgical rotational cutting tools such as rotary initiator devices (also known as a canal initiator tips), or straight reamers.

To form thedrill bit10, there may first be provided a work piece that comprises theshaft4 of thedrill bit10, with ahead portion46. In the present example, the head portion has a curved outer surface, the remaining parts of which (i.e. following the formation of theflutes12A,12B,12C,12D) will subsequently form the bone contactingouter surface20 of the drill bit. Afirst part54 of the curved outer surface may be substantially spherical. Following the formation of theflutes12A,12B,12C,12D, remaining parts of a distal part of thefirst part54 of the curved outer surface may subsequently form thecurved portion21 of the bone contactingouter surface20 that curves inwards toward thelongitudinal axis5 as it approaches the pointeddistal tip8. A proximal part of thefirst part54, andsecond part58 of the curved outer surface of thehead portion46 may together subsequently form theneck18 of thedrill bit10.

Thehead portion46 may also include a distalconical portion56. The distalconical portion56 may extend distally from thefirst part54 of the curved outer surface of thehead portion46. An apex48 of the distalconical portion56 may lay on thelongitudinal axis5. Following the formation of theflutes12A,12B,12C,12D, a remaining part of the distal conical portion56 (perhaps including the apex48) may subsequently form the distalpointed tip8 of thedrill bit10.

To form theflutes12 of thedrill bit10, a tool such as a cylindrical milling cutter or ball nose cutter may be used to remove material from thehead portion46.

For instance, the use of a cylindrical milling cutter can give rise toflutes12 that have surfaces that are concave and the shape of a partial cylinder. One cut may be made by the cylindrical milling cutter perflute12, with each cut being circumferentially spaced around thehead portion46 at positions corresponding to the desired locations of theflutes12. The cylindrical milling cutter may be oriented at an angle θ with respect to thelongitudinal axis5. Consequently, a cylindrical axis of the concave cylindrical surface of eachflute12 may be oriented at an angle in therange 20°≤θ≤80° with respect to thelongitudinal axis5. It is envisaged that a ball nose cutter may instead be used to formflutes12 that have surfaces that are concave and the shape of a partial cylinder.

As noted previously, it is envisaged that the flutes may have a concave cross-sectional shape other than that of a partial cylinder. For instance, the concave surface may be a V-shaped (with the apex of the “V” pointing inwards, towards the longitudinal axis5), or square-shaped). These, and other cross sectional shapes for the concave surfaces of the flute may be made using an end mill cutter. An axis of these flutes, analogous to the cylindrical axis noted above, may be oriented at an angle in therange 20°≤θ≤80° with respect to thelongitudinal axis5 of the drill bit.

Although in the examples shown in the Figures the path of eachflute12 as it extends proximally from thedistal tip8 is substantially straight, it is also envisaged that the path may be curved. For instance, the path may be substantially helical and/or may curve toward or away from thelongitudinal axis5.

It is also envisaged that eachflute12 may be tilted or angled in one direction to create edges with different angles at either side of the groove formed by eachflute12. This may allow the cutting edges of eachflute12 to have a preferential rotation cutting direction compared to the opposite rotational direction. Moreover, the groove shape or tilt may change across the surface of thehead6, to further vary the edge angle.

FIGS. 5A to 5D show a number of views (cross sections) of thesurgical drill bit10 of the drill bit ofFIGS. 1 to 3, each cross section taken in a plane perpendicular to thelongitudinal axis5.

FIG. 5A shows a distal view of thehead6. FromFIG. 5A, it can be seen that thedrill bit10 in this example includes fourflutes12A,12B,12C,12D circumferentially positioned at 90° intervals around thehead6. Consequently, thedrill bit10 includes fourcutting edges30, which are also positioned at 90° intervals around thehead6. The V-shapedrespective parts34 of thecurved portion21 of the bone contactingouter surface20 are also visible inFIG. 5A, showing how thesepart34 curve inwards toward thelongitudinal axis5 as they approach the pointeddistal tip8, thereby to make theapexes36 less prominent.

FIG. 5B shows a cross section through thehead6 at a position along thelongitudinal axis5 intermediate the pointeddistal tip8 and theapexes36. The curved (e.g. substantially cylindrical) shape of the surfaces of theflutes12A,12B,12C,12D are visible inFIG. 5B.

FIG. 5C shows a cross section through thehead6 at a position along thelongitudinal axis5 proximal theapexes36. The curved (e.g. substantially cylindrical) shape of the surfaces of theflutes12A,12B,12C,12D is again visible inFIG. 5C.

FIG. 5D shows a cross section through thehead6 at a position along thelongitudinal axis5 further proximal theapexes36 with respect to the cross section ofFIG. 5C. The curved (e.g. substantially cylindrical) shape of the surfaces of theflutes12A,12B,12C,12D is once again visible inFIG. 5C.

In some examples, the drill bit may include a plurality of further cuttingedges38 that are located on theshaft4 intermediate thehead6 and theproximal end2. These further cuttingedges38 may be used to make lateral cuts into the bone at a position located proximally with respect to thehead6. An example of the use of adrill bit10 including further cuttingedges38 will now be described in relation toFIG. 6.

As can be seen inFIG. 6, the drill bit in this example is substantially as described above in relation toFIGS. 1 to 5, with the addition of the plurality of further cutting edges38. It is envisaged that the drill bit may instead of the kind to be described below in relation toFIGS. 7 to 11 (again, with the addition of thefurther cutting edges38 on the shaft4).

To use thefurther cutting edges38, they may be urged laterally against the surface of the bone, as indicated schematically inFIG. 6 by the arrows labelled B. Typically, this may be done after thehead8 has been used to drill into the bone along a direction parallel to thelongitudinal axis5, as indicated inFIG. 6 by the arrow labelled A. In some examples, thefurther cutting edges38 may be used to widen an initial opening in the bone made by thehead6. When performing the lateral movements B for urging thefurther cutting edges38 laterally against the surface of the bone, it will be appreciated that thehead6 may be located inside the bone.

As described above, thehead6 of thedrill bit10 is configured such that it does not cut laterally into a bone when the drill bit is moved laterally. Where thedrill bit10 includes thefurther cutting edges38 for making lateral cuts into the bone at a position located proximally with respect to thehead6, the fact that thehead6 is so configured may allow thefurther cutting edges38 with confidence, in the knowledge that this is unlikely to result in unwanted lateral cuts by thehead6.

In one particular example, a surgical rotational cutting tool such as thedrill bit10 may be used to prepare a femur to receive a stem of a femoral prosthetic during a hip replacement procedure. In this example, after cutting away the head and neck of the femur, a drill having asurgical drill bit10 of the kind described above attached thereto is used to drill through a proximal cut surface of the femur to gain access to the medullary canal. Thereafter, the surgeon may position thedrill bit10 so that thehead6 is located inside the medullary canal, while thefurther cutting edges38 are located at the entrance to the medullary canal. Thefurther cutting edges38 may then be used to remove bone from the medullary canal, by moving thedrill bit10 laterally as described in relation toFIG. 6. This may allow the medullary canal to be shaped to receive the stem. For instance, thefurther cutting edges38 may be used to widen the entrance to the medullary canal. In one example, thefurther cutting edges38 may be used to remove parts of the piriformis fossa and/or at least part of the greater trochanter that remains after the removal for the femoral neck and head. While thefurther cutting edges38 are being used as described above, thehead6 may be located inside the medullary canal. As described above, the configuration of thehead6 may allow thefurther cutting edges38 to be used effectively, without causing unwanted lateral removal of bone from the medullary canal by thehead6.

FIG. 7 shows a side view of asurgical drill bit10 for a bone drill according to another embodiment of this invention. An isometric view of thedrill bit10 is shown inFIG. 8.FIG. 9 shows a detailed view of thehead6 of thedrill bit10.

The drill bit in this example is similar to the one described above in relation toFIGS. 1 to 5, with the exception that it does not include a narrowedneck18 of the kind included in that earlier example. Accordingly, in this example, the bone contactingouter surface20 does not include a proximal portion that curves inwards toward thelongitudinal axis5 with increasing distance from the pointed distal tip8 (thereby to form aneck18 of the kind shown in the embodiment ofFIG. 3). Instead, thecurved portion21 of the bone contactingouter surface20, which curves inwards toward thelongitudinal axis5 as it approaches the pointeddistal tip8, may terminate proximally at the base of the head, where it meets the outer surface of theshaft4.

In other respects, the configuration of thehead6 in the embodiment ofFIGS. 7 to 9 may be similar to that described above in relation to the embodiment ofFIGS. 1 to 3.

FIG. 10 illustrates a stage in the manufacturing of the surgical drill bit ofFIGS. 7 to 9, prior to the formation of theflutes12A,12B,12C,12D. Again, it is envisaged that the same or a similar approach may be used for manufacturing other surgical rotational cutting tools such as rotary initiator devices (also known as a canal initiator tips), or straight reamers.

To form thedrill bit10, there may first be provided a work piece that comprises theshaft4 of thedrill bit10, with ahead portion66. In the present example, thehead portion66 has a curvedouter surface64, the remaining parts of which (i.e. following the formation of theflutes12A,12B,12C,12D) will subsequently form thecurved portion21 of the bone contactingouter surface20 of thedrill bit10. The curvedouter surface64 may be substantially spherical (i.e. it may correspond in shape to a portion of the surface of a sphere).

Thehead portion66 may also include a distalconical portion66. The distalconical portion66 may extend distally from the curvedouter surface64. An apex48 of the distalconical portion66 may lay on thelongitudinal axis5. Following the formation of theflutes12A,12B,12C,12D, a remaining part of the distal conical portion66 (perhaps including the apex48) may subsequently form the distalpointed tip8 of thedrill bit10.

Starting with the work piece shown inFIG. 10, a cylindrical milling cutter or a ball nose cutter may be used substantially as described above in relation toFIG. 4 to form theflutes12, resulting in adrill bit10 of the kind shown inFIGS. 7 to 9. Again, in embodiments in which theflutes12 are V-shaped or square, then an end mill cutter may be used to form theflutes12 instead.

FIG. 11A to 11D show a number of views (cross sections) of thesurgical drill bit10 of the drill bit ofFIGS. 7 to 9, each cross section taken in a plane perpendicular to thelongitudinal axis5. The views (cross sections) inFIGS. 11A to 11D are at the same positions along thelongitudinal axis5 as those inFIGS. 5A to 5D. Comparison of the views inFIGS. 5A to 5D with those inFIGS. 11A to 11D demonstrate that thehead6 of thedrill bit10 of this second embodiment is similarly configured to thehead6 in the first embodiment, at least in positions distal the proximal end of thecurved portion21.

The surgical rotational cutting tools described herein may comprise a material such as stainless steel. By way of example, 400 or 600 series stainless steel cold be used (e.g. 17/4 PH (600 series); 420 S29/S45; 440 B, or 440C).

Embodiments of this invention can allow the functions of a pointed tip for initially drilling into a bone, and a lateral reamer, to be combined in a single tool. This can save manufacturing costs in the production surgical instruments for performing a surgical procedure, and can reduce the weight and size of a surgical kit incorporating the drill bit.

According to embodiments of this invention, a surgical kit may be provided. The kit may, for instance be a kit for a hip replacement procedure. The kit may include a plurality of surgical rotational cutting tools (e.g. drill bits) of the kind set out above. It is envisaged that some of the surgical rotational cutting tools may be of different sizes.

Accordingly, there has been described a surgical rotational cutting tool, a surgical kit and a method of preparing a femur to receive a stem of a femoral prosthetic. The tool includes a longitudinal axis and a shaft extending along the longitudinal axis, which has a proximal end and a distal end. The tool also includes a head located at the distal end of the shaft. The head includes a pointed distal tip, a bone contacting outer surface having a portion which curves inwards toward the longitudinal axis as it approaches the tip, and a plurality of flutes. The edges of distal parts of neighbouring pairs of the flutes meet to define a plurality of cutting edges which extend proximally from the pointed distal tip. A proximal part of each flute extends proximally across the curved portion.

Although particular embodiments of the invention have been described, it will be appreciated that many modifications/additions and/or substitutions may be made within the scope of the claimed invention.

Claims (16)

The invention claimed is:

1. A surgical rotational cutting tool comprising:

a longitudinal axis;

a shaft extending along the longitudinal axis and having a proximal end and a distal end; and

a head located at the distal end of the shaft, the head comprising:

a pointed distal tip;

a bone contacting outer surface having a curved portion which curves inwards toward the longitudinal axis as it approaches the tip; and

a plurality of flutes positioned circumferentially around the head, wherein each flute includes a proximal part and a distal part, wherein each distal part extends proximally from the pointed distal tip, wherein edges of the distal parts of neighboring pairs of said circumferentially positioned flutes meet to define a plurality of cutting edges which extend proximally from the pointed distal tip, and wherein the proximal part of each flute extends proximally across the curved portion of the bone contacting outer surface; wherein an angle(s) at which the edges of the distal parts of said neighboring pairs of flutes meet to define the plurality of cutting edges are more acute than an angle(s) at the edges formed between the proximal part of each flute and the bone contacting outer surface.

2. The surgical rotational cutting tool ofclaim 1 comprising a plurality of further cutting edges located on the shaft intermediate the head and the proximal end of the shaft.

3. The surgical rotational cutting tool ofclaim 1, wherein the cutting edges extending proximally from the pointed distal tip are concave.

4. The surgical rotational cutting tool ofclaim 1, wherein each flute comprises a concave surface.

5. The surgical rotational cutting tool ofclaim 4, wherein an axis of the concave surface of each flute is oriented at an angle in the range 20°≤θ≤80° with respect to the longitudinal axis.

6. The surgical rotational cutting tool ofclaim 4, wherein the concave surface of each flute is a concave cylindrical surface.

7. The surgical rotational cutting tool ofclaim 1, wherein the proximal parts of respective neighboring pairs of flutes are separated from each other by a respective part of the curved portion of the bone contacting outer surface.

8. The surgical rotational cutting tool ofclaim 7, wherein each respective part of the curved portion of the bone contacting outer surface is substantially V-shaped, and wherein the apex of each substantially V-shaped part meets a proximal end of the cutting edge that is defined by said respective neighboring pair of flutes.

9. The surgical rotational cutting tool ofclaim 1, wherein the bone contacting outer surface has a proximal portion that curves inwards toward the longitudinal axis with increasing distance from the pointed distal tip, to form a neck of the surgical rotational cutting tool.

10. The surgical rotational cutting tool ofclaim 9, wherein the proximal part of each flute extends proximally across the proximal portion of the bone contacting outer surface.

11. The surgical rotational cutting tool ofclaim 1, wherein at least part of the bone contacting outer surface is substantially spherical.

12. The surgical rotational cutting tool ofclaim 1 wherein the flutes are equally circumferentially spaced around the head.

13. The surgical rotational cutting tool ofclaim 1 comprising four of said flutes.

14. The surgical rotational cutting tool ofclaim 1, wherein the tool is a surgical drill bit, rotary initiator device, or a straight reamer.

15. A surgical rotational cutting tool comprising:

a longitudinal axis;

a shaft extending along the longitudinal axis and having a proximal end and a distal end; and

a head located at the distal end of the shaft, the head comprising:

a pointed distal tip;

a bone contacting outer surface having a curved portion which curves inwards toward the longitudinal axis as it approaches the tip; and

a plurality of flutes positioned circumferentially around the head, wherein each flute includes a proximal part and a distal part, wherein each distal part extends proximally from the pointed distal tip, wherein edges of the distal parts of neighboring pairs of said circumferentially positioned flutes meet to define a plurality of cutting edges which extend proximally from the pointed distal tip, and wherein the proximal part of each flute extends proximally across the curved portion of the bone contacting outer surface; wherein the cutting edges extending proximally from the pointed distal tip are concave.

16. A surgical rotational cutting tool comprising:

a longitudinal axis;

a shaft extending along the longitudinal axis and having a proximal end and a distal end; and

a head located at the distal end of the shaft, the head comprising:

a pointed distal tip;

a bone contacting outer surface having a curved portion which curves inwards toward the longitudinal axis as it approaches the tip; and

a plurality of flutes positioned circumferentially around the head, wherein each flute includes a proximal part and a distal part, wherein each distal part extends proximally from the pointed distal tip, wherein edges of the distal parts of neighboring pairs of said circumferentially positioned flutes meet to define a plurality of cutting edges which extend proximally from the pointed distal tip, and wherein the proximal part of each flute extends proximally across the curved portion of the bone contacting outer surface; wherein each flute comprises a concave surface.

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